1. Field of the Invention
The present invention relates to a process for producing a random copolymer which comprises propylene and a specific diene as essential components and has an unsaturated carbon-carbon bond.
More particularly, the present invention relates to a process for preparing a novel propylene-based random copolymer which has excellent formability/moldability, heat resistance, transparence, impact resistance and stiffness and has reactivities such as crosslinking ability, paintability, and printability.
2. RELATED ART
It is well known that the homopolymers or copolymer of propylene have excellent properties, whereby their applications to a variety of fields have been developed.
On the other hand, these polymers are essentially saturated hydrocarbons in nature and have poor chemical reactivities. Consequently, they are accompanied by problems such as limitation in grafting or crosslinking and distinguished inferiority in adhesion, paintability, printability and the like which require polar groups.
Various inventions have been proposed for the purpose of overcoming these disadvantages. Among these inventions the followings are particularly related to the present invention: Japanese Patent Application Laid-Open Publication Nos. 165907/80, 30414/81, 36508/81, 115007/87 and 115008/87. These inventions relate to the copolymerization of propylene and a 1,4-diene. The product is valuable as a reactive polypropylene because of an unsaturated double bond in its side chains.
However, one of the problems of these inventions is, so far as the present inventor knows, that an expensive 1,4-diene must be used in a large amount as the 1,4-diene does not necessarily have a high copolymerizability. They have also a problem in that a 1,4-diene having a low reactivity must be charged into a polymerization system in a large amount, so that the catalyst activity is low, and thus the cost of the catalyst tends to be high.
Further, in Japanese Patent Application Laid-Open Publication No. 36508/81 is disclosed a process for prepolymerizing propylene in the copolymerization of a 1,4-diene and propylene. The process had, so far as the present inventor knows, a problem in that a gel of a crosslinked polymer which is insoluble in decalin at 35.degree. C. was often produced due to the presence of the 1,4-diene. In addition, a serious problem in the polymerization operation was that when prepolymerization and polymerization are conducted in one reactor, the 1,4-diene does not necessarily have a high copolymerizability, so that a large amount of the 1,4-diene must be added within a short period of time after prepolymerization in order to increase the concentration of the 1,4-diene.
Also, Japanese Patent Application Laid-Open Publication No. 155416/84 discloses a process for preparing a block copolymer which has a non-conjugated branched diene as an essential component. However, so far as the present inventor knows, the process had a problem of low transparence of the product notwithstanding the good impact resistance. Moreover, the diene utilized in examples had low polymerizability per se and copolymerizability and thus required improvement in both the cost, especially that involved in catalysts used, and the operation, especially that which entails supplementing a large amount of the diene.